about the kt 120 tube

It's a tube made in Russia just like Sovtek and Electro Harmonics. In this case, it's branded Tung Sol. I believe the Chinese might be trying to make a copy of this tube. I don't see the price dropping very much for this tube, I'm just guessing. It uses heavier glass and is a more robust version on the 6550. It is NOT a drop in replacement for the 6550.

Wow. Egg output tubes. Who knows. The Russians never stop designing tubes so it wouldn't surprise me.

The reason the Chinese haven't copied the Russians might have something to do with their raw materials and their technology. They are behind the Russians on both. After the issues with the first 6550's out of China many years ago, I am wary of them and therefore stay away from them. That being said, the only Chinese tubes I found to be exceptionally good were the EL-34 Treasures. That's about it.

I have not tried those. I currently use the JJ ECC803S. I find it to be very quiet and good sounding. I know some people have had issues with them. So far no issues...